1. Field of the Invention
The present invention relates to a vehicle power supply device that includes serially connected battery cells.
2. Description of Related Art
A drive system for an vehicle rotating electrical machine is provided with a secondary battery for supplying DC power and an inverter device that converts the DC power supplied from the secondary battery to three-phase AC power. The three-phase AC power is supplied to the rotating electrical machine installed in the vehicle. A three-phase AC rotating electrical machine generally includes a function as an electric motor and a function as a power generator. If a three-phase AC rotating electrical machine is operated as a power generator such as in regenerative braking operation, the three-phase AC power generated by the rotating electrical machine is converted to DC power by the inverter device. The DC power is supplied to the secondary battery. The generated power is stored in the secondary battery.
A lithium battery module is suitable for a secondary battery because a large amount of power can be stored in a small-sized module. A lithium battery module includes numerous serially connected lithium battery cells. It is necessary to individually detect the state of each of the lithium battery cells and to monitor whether or not an abnormality has occurred.
There is a vehicle DC power supply device including a lithium battery disclosed in, for instance, Japanese Laid Open Patent Publication No. 2005-318751.
A normal circuit is essential for monitoring the state of individual lithium battery cells. The state of a lithium battery is usually monitored based upon a measured terminal voltage at a lithium battery cell. Accordingly, an abnormality in the measurement circuit for measuring a terminal voltage at a lithium battery cell may cause difficulty in monitoring the state of the lithium battery.